https://www.theregister.co.uk/2019/09/11/windows_cpu_cortana/

Microsoft's build 18362.356 (KB4515384​​​​​) for its Windows 10 May 2019 Update (version 1903) rolled out on Tuesday with security improvements for Internet Explorer, Microsoft Edge, networking tech and input devices – and a CPU usage fix that, for some, has broken desktop search.

The security tweaks address a variety of speculative execution side-channel vulnerabilities known as microarchitecture data sampling (MDS) for 32-bit x86 versions of Windows. Intel dealt with the CVEs at issue – CVE-2019-11091, CVE-2018-12126, CVE-2018-12127, CVE-2018-12130 – in May.